1. Field of the Invention
The present invention relates to the design of semiconductor devices and the analysis of defects thereof and, more particularly, to an error detecting circuit for quickly detecting the location of an error in a semiconductor chip before the semiconductor chip is provided to a user.
2. Description of the Related Art
As the number of transistors integrated in a semiconductor chip increases, significantly more time and efforts are required for testing the semiconductor chip, which raises the manufacturing cost of the semiconductor chip. In testing a chip, both design error and manufacturing process error should be detected. In particular, it is technically very difficult and takes a significant amount of time to detect a chip that does not operate normally because of a tolerance corresponding to a manufacturing process, although the design of the chip has no problem at all.
Such chips having defects caused by design and manufacturing processes should be detected before shipping. For this, generally, design engineers prepare test vectors for detecting these defects when the chips are designed, and test engineers check for defects of the manufactured chips with the prepared test vectors. In principle, the test vectors should be prepared so that all possible defects that may occur in the design and manufacturing processes can be detected. In reality, manufacturers try to reduce costs by performing tests using only a minimum number of test vectors. After taking tests based on the minimum number of test vectors, these chips are provided to users. When these chips are used by users, defects which were not detected during the tests may occur. In this case, manufacturers should add test vectors for detecting these defects to the existing test vectors so that they can be detected during the tests.
To find the causes of these defects, design engineers reproduce these defects through computer simulation in which conditions that are presumed to be the cause of these defects in the circuit design are input. Through computer simulation, the design engineers check the causes and locations of these defects. If a design error causes the defects, then the chip design should be revised. If a tolerance of the manufacturing process causes the defects, then the design should be revised or the testing performed with additional test vectors, upon estimating which course of action is the most cost effective.
To accurately find the causes and locations of defects through computer simulation, significant simulation time and design engineers' efforts for analysis are needed. Also, computer simulation does not guarantee that the causes and locations of defects will be found with 100% accuracy. Therefore, it is very important to determine through the operating characteristics of a semiconductor chip, that is, the operating characteristics of hardware, where and why defects occur in a circuit. Unless design engineers consider these points, losses in time and costs can be incurred.
In particular, chips manufactured based on a circuit design drawn by a design tool that automatically generates a circuit design have a more serious problem. After taking tests using the minimum basic test vectors, these chips are determined to be normal chips and shipped to users. However, when users are using these chips, defects may occur and it is very difficult to find the causes and locations of defects in these chips.